This paper systematically reviews ex-post empirical studies assessing the effects of climate change mitigation policies on emissions. It synthesises evidence from 187 studies covering five broad sectors – agriculture, forestry and land use; buildings; industry; power; and transport – providing about 450 estimates of policy impact. Estimates are harmonised to ensure comparability and expressed as annual percentage changes in emissions relative to a no-policy scenario. 

The findings suggest that most policies effectively reduce emissions, with a median effect of about -5% per year, though with substantial variation across studies. The results exhibit significant heterogeneity across policy instruments, sectors and regions, reflecting differences in policy design, implementation and contextual factors. The analysis highlights key evidence gaps and lays the foundation for future meta-analytical work on the determinants of policy effectiveness.